Previous methods of packaging spoilable material have involved packing the product within a plastic bag or the like, evacuating the bag, with the outside of the bag exposed to atmospheric pressure as the vacuum is applied, then injecting gas or gas mixture in place of the air.
This has been carried out using vacuum packing machinery. An example of this is described in U.S. Pat. No. 3,939,624. However, that method and other existing vacuum packing systems are not entirely satisfactory for all applications.
A particular problem found with vacuum packing systems where the bag is exposed to atmospheric pressure, is that the moment that vacuum is drawn on the bag, whilst the neck of the bag is clamped about the "snorkel" or other connecting passageway, the bag rapidly collapses under the pressure differential between the atmosphere on the outside of the bag and the partial pressure within the bag. Pockets of air are often trapped within the bag and cannot be evacuated by the passageway, as the bag collapses between the pocket of air and the end of the passageway. Thus if a gas is injected into the bag prior to sealing, it will be mixed with a proportion of air remaining within the bag. This is undesirable, as the remaining air can expose the product, eg meat, to excess oxygen resulting in spoilage.
This problem can be avoided to some extent by providing a snorkel which projects far enough into the bag to contact the product inside, such that the bag can not collapse between the mouth of the snorkel and the product. However, this does not prevent air entrapment at the far corners of the bag or between the bag and the product.
Furthermore, the use of a long snorkel projecting this far into the bag can make sealing of the bag more complicated and time consuming.